Otitis media with effusion (OME), or serous otitis media, is a common condition in children and frequently leads to deafness at a critical age of development. The broad objective of this research is to study OME in order to elucidate the pathogenesis of this condition in humans and develop a suitable animal model. The immediate goals of this study are: (1) to clarify the role of subclinical infection in OME pathogenesis, (2) to clarify the factors, such as antimicrobial agents (lysozyme and immunoglobulins), that modify the bacterial infection in the middle ear, and (3) to devise practical diagnostic laboratory procedures fr detecting hidden infection. Middle ear effusions and mucosal biopsy from the patient with OME will be investigated by immunochemistry, microbiology, cytochemistry, and electron microscopy. An attempt will be made to test the following hypotheses in an animal model: (1) Initial infection of the ear that was inadequately treated by antibiotics causes disturbances of immunity formation of the ear and the subsequent infection causes OME. (2) Primary infection and introduction of bacterial antigens produce sensitization of tubal and middle ear mucosa, and subsequent infection results in immediate and/or delayed hypersensitivity.